1.Field of the Invention
This invention relates to combustors and in particular to turbojet combustors that are capable of controlling and reducing nitric oxide emissions during operation by buring a major portion of the fuel in a secondary combustion zone wherein emission products from a primary combustion zone are used as an ignition source under conditions that result in low nitric oxide emissions.
Recent environmental considerations have advanced the research for an efficient and dependable turbojet combustor that is capable of reducing and controlling nitric oxide emissions and which is at the same time resistant to problems such as flame stability and engine failure which can occur at temperatures sufficiently low to reduce nitric oxide emissions. The present invention efficiently controls such emissions while assuring flame stability by providing a secondary combustion zone in which combustion takes place at abnormally low temperatures in a novel turbojet combustor under catalyzed conditions that reduce and control nitric oxide emissions while obviating the conditions coupled with the efficient method for the control of nitric oxide emissions is particularly advantageous where thrust and/or weight considerations are important such as in jet aircraft or light automobiles.
2. Description of the Prior Art
It is known in the combustor art that operation of a combustor at or near stoichiometric fuel-air proportions results in a combustion that is resistant to flame-out characteristics but results in the undesirable emission of high quantities of oxides of nitrogen. Combustion at substantially less than stoichiometric proportions results in lower nitric oxide emissions as a result of lower combustion temperatures but these conditions encourage engine failure due to flame-outs.
Work on the development of a combustor capable of controlling and reducing nitric oxide emissions has resulted in a variety of combustor designs and various methods for mixing fuel and air to control the manner and temperature of combustion. In addition, staged combustors, that is combustors having more than one fuel burning chamber, have been developed that in operation generally burn fuel in both chambers at or about stoichiometric proportions and then rely upon elaborate circulation patterns to provide a non-adiabatic process between the stages to remove or transfer heat to keep the temperatures sufficiently low to control nitric oxide emissions. Other staged combustors have employed elaborate fuel flow and air recirculation patterns in conjunction with non-adiabatic heat transfers within the combustor in an effort to reduce nitric oxide emissions.
The present invention does not rely on non-adiabatic processes or complex mixing procedures in providing a low level of nitric oxide emissions. The present invention controls nitric oxide emissions while providing flame stability by employing a novel turbojet combustor arrangement and a method of burning fuel therein. More particularly the present invention achieves its advantages by providing a multiple zone combustor and method of buring fuel therein so that a primary combustion zone is operated at fuel rich conditions to provide flame stability from which combustion products of the primary zone are introduced and used as a catalyst in a secondary combustion zone in an adiabatic process with a second portion of fuel and air introduced therein to provide a fuel-lean and low temperature combustion that controls nitric oxide emissions.